1. Field of the Invention
The invention disclosed herein relates to a previously unknown method and improved process for producing a continuous bundle of small diameter, extremely fine fibers of a blend or dispersion of two polymers, one of which is not normally considered to be a fiber-forming polymer. This invention additionally pertains to the compositions and the dispersions or blends thereof from which the fibers of the invention may be formed by a fibrillation process. More specifically, the invention relates to a process for obtaining extremely fine polyamide/polystyrene fibers by fibrillation from an extruded blend consisting of a polyamide and a polystyrene, said blend being limited to a very specific and narrow range of polyamide and polystyrene.
2. Description of the Prior Art
In the prior art, it is known to blend or mix polymers and copolymers and then form or produce filaments from the mixture or blend by extruding the molten blend or a solution of the blend either through a conventional die orifice or a spinneret, as for instance disclosed in U.S. Pat. No. 3,330,899 to Fukushima et al. The prior art also discloses the producing of a noncontinuous fibril within a filament by extruding a dispersion of two immiscible materials and then drawing the extrudate. Additionally, it is known to extrude a mixture or dispersion of two materials, then extract one of them to form a microporous filament. It is also known in the prior art to make filaments or fibers by extruding a sheet, film, strand or monofilament of the fiber-forming material, then optionally treating it with a solvent to weaken the same at crystal cleavage points and finally mechanically breaking the structure into noncylindrical fibers. However, no process or composition is disclosed in the prior art which creates a continuous fibril mass of crystalline oriented, extremely fine fibrils which without resort to carding can be easily twisted into yarn. Most of the processes and methods of the prior art that require or make use of a mechanical beating or breaking up of an extruded sheet, film, strand or monofilament result in a noncylindrical, sharp-edged and irregular fibers. Other known processes and methods are limited to fibers of a size proportional to the orifice through which they are extruded.
It is additionally known in the prior art to fibrillate thermoplastic, uniaxially oriented films or tapes of polyethylene, polypropylene, nylon and other materials by stretching and annealing of the thermoplastic film under specific conditions of temperature, draw ratio and annealing temperature, then passing the drawn film across or through a mechanical working means so that the uniaxially oriented film is rubbed, twisted, braided, scraped or punctured or a combination of these actions to cause fibrillation of the film. It has also been disclosed that sonic means such as a sonic probe may be used to cause fibrillation of drawn film.
However, certain thermoplastic films or strands such as nylon, even when drawn, are very difficult to fibrillate. When these nylon structures are subjected to the fibrillation techniques of the prior art, they often break rather than fibrillate because the tension of the film or strand across the fibrillator must be great in order to get a severe enough action with the prior known fibrillators to fibrillate the film or strand. Nylon strands, monofilaments, tapes, sheets and films prepared by the previously known methods and those taught in the prior art are difficult to fibrillate except under extreme conditions. These nylons must normally be uniaxially oriented by stretching under specific conditions of temperature, draw ratio and annealing temperatures and then subjected to severe mechanical workings in order that they may be fibrillated at all. However, the nylon structures prepared by the methods of this invention and from the blended compositions thereof can be readily fibrillated by the processes of this invention which are much simpler and more economical than many of the conventional methods previously employed and taught by the prior art.